JPH0467817B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a communication method applied to signal transmission and reception between communication devices connected by a two-wire transmission path.

[Conventional technology]

In industrial processes, etc., when remotely controlling valves, etc., a receiving device generally called a positioner is installed, and for example, 4 to 20
A signal is transmitted using a current value that varies depending on the range of mA, and a receiving device receives the signal and performs control according to the current value.

However, since signals are transmitted only by analog current values, it is not possible to transmit two data at the same time, and it is also difficult to transmit control monitoring signals etc. to the control device. In this case, separate transmission lines and transmission equipment must be provided, and when transmitting and receiving two sets of data at the same time on the control equipment side, two transmission lines and equipment must be provided in each direction. It has become necessary to provide each.

[Problem that the invention seeks to solve]

Therefore, in the past, when transmitting and receiving two pieces of data at the same time, equipment costs were high, the number of parts subject to maintenance and inspection increased, and the number of maintenance steps increased. It is occurring.

The present invention has an object of fundamentally solving the above-mentioned conventional problems, and provides an extremely effective communication device capable of transmitting and receiving two pieces of data at the same time.

[Means for solving problems]

Therefore, the object of the present invention is achieved by the following configuration.

That is, in the present invention, in a communication device in which a first communication device and a second communication device are connected via a two-wire transmission path to transmit and receive signals, the first communication device (FIG. 2) A composite signal obtained by superimposing a pulse signal of a predetermined code corresponding to the second transmit data SA ₂ on an analog signal with a value within a predetermined range corresponding to the first transmit data SA ₁ is sent to the two-wire transmission line L to increase the line current. The transmission means A ₁ and Q ₁ supply the data as changes in value, and the line voltage V _L of the two-wire transmission line is detected, and the third transmission data SB is sent from the second communication device from this detection output. The _second communication device (FIG. 3) consists of receiving means A ₂ , INT ₁ , and FL ₁ that separate and output an analog signal according to the fourth transmission data SB ₂ and a pulse signal according to the fourth transmission data SB 2 . detects the line current of the two-wire transmission line and outputs an analog signal according to the first transmission data sent from the first communication device and a pulse signal according to the second transmission data from the detection output. a receiving means Rs, INT ₂ , FL ₂ that separates and outputs the
Transmitting means A that supplies a composite signal in which a pulse signal of a predetermined code corresponding to the fourth transmission data is superimposed on an analog signal corresponding to the third transmission data to the two-wire transmission line as a change in the line voltage value. ₁₁ , _Q11 , _A12 ,
It is composed of Q ₁₂ .

[Effect]

Therefore, a total of four pieces of data can be transmitted between the two communication devices through the same transmission path using analog values and digital changes in the line current and line voltage, respectively.

〔Example〕

Hereinafter, details of the present invention will be explained with reference to figures showing examples.

FIG. 2 is a block diagram showing the first communication device, in which the serial digital signal transmission data SA ₁ is transmitted directly, and the analog signal transmission data SA ₂ is transmitted directly.
Through digital converter (hereinafter referred to as ADC) A/D ₁ ,
The signals are sent to the control unit CNT ₁ , which includes a processor such as a microprocessor, memory, etc., where each signal is converted into an analog value or a coded pulse signal, and the pulse signal is superimposed on the analog value. For example, if the transmission data SA ₁ is an analog value within a predetermined range, the transmission data
SA ₂ becomes a pulse signal indicated by a predetermined code, and the composite value of these is sent to a differential amplifier via a digital-to-analog converter (hereinafter referred to as DAC) D/A ₁ .
Sent to _A1 .

Then, the amplifier A ₁ changes the collector of the transistor Q ₁ according to the analog output of the DAC/D/A ₁ .
In order to control the impedance between emitters, a line L ₁ , which constitutes a two-wire transmission line (hereinafter referred to as a transmission line) L,
The value of the line current I _L sent from the power source E to the transmission line _L changes according to the impedance change of the transistor Q ₁ connected in series with the power source E between the line terminals t ₁ and t ₂ connected to L 2. do.

However, on the emitter side of transistor _Q1 ,
A resistor R _f is inserted, and the terminal voltage of this is given as negative feedback to the differential amplifier A ₁ , so that the value of the line current I _L is changed to the DAC.
It is designed to be stabilized to a value according to the output of D/A ₁ .

Therefore, as shown in FIG. 1, which shows the changes in the line current I _L and line voltage V _L of the transmission line L, the line current I _L is, for example, within the range of 4 to 20 mA, an analog signal corresponding to the transmission data SA ₁ . value, and
On the other hand, it exhibits a superimposed digital change,
This indicates the transmission data _SA2 .

In this example, the pulse-like digital changes are made to have approximately the same value in both the positive and negative directions, and one cycle of change from negative to positive changes the logic value to "0", and one cycle of change from positive to negative It is assumed that the same "1" is indicated depending on the cycle.

In addition, as will be described later, the line voltage V _L is also determined to have an analog value and a digital change depending on the transmission by the second communication device, and in this example, the change value in the positive and negative directions is the same as described above. On the other hand, a two-cycle change indicates, for example, a logic value of "1", and no change indicates a similar "0".

Therefore, for the purpose of detecting analog _values and digital changes in the line voltage V _L , a high input impedance differential amplifier A ₂ is provided in FIG. detect,
This detection power is averaged by the integrator circuit INT ₁ to remove digital changes, and an analog value is obtained, which is converted to a digital signal by ADC/A/D ₂ , and then applied to the control unit CNT ₁ . A digital variation component is separated from the comparison output by a waveform unit FL ₁ that passes the frequency component of the variation, and is applied to the control unit CNT ₁ as a serial digital signal via the waveform shaper WF ₁ .

Therefore, the control unit CNT ₁ performs conversion and decoding processing according to these inputs,
For example, in response to an analog value, the serial digital signal reception data RA ₁ is sent out, and in response to a digital change, the analog signal reception data RA ₂ is sent out via the DAC/D/A ₂ .

The device shown in FIG. 2 is generally installed on the central control device side, so power is supplied to each section from the corresponding power supply section.

FIG. 3 is a circuit diagram showing a second communication device installed together with field equipment, etc.
It is connected to the transmission line L in Fig. 2 via t ₁ and t ₂ , and the emitter and collector of a transistor Q ₁₁ is inserted in series with it, and a receiver is connected to the collector side of this. Resistor Rs is connected in series, while resistors R ₁ , R ₂ are connected in parallel with these.
A voltage dividing circuit is connected thereto, and a series circuit formed between the emitter and collector of resistor _R3 and transistor _Q12 is connected.

Further, in parallel with the transistor Q ₁₂ , as a load circuit, differential amplifiers A ₁₁ and A ₁₂ , a voltage dividing circuit including resistors R ₄ to R ₇ , DAC/D/A ₁₁ to D/A ₁₃ , ADC/
A/D ₁₁ , A/D ₁₂ , control unit similar to control unit CNT ₁
CNT ₂ , comparator CP ₂ , and waveform shaper WF ₂ are connected, and control unit CNT ₂ is connected to DAC/D/D/
Reference voltages Vr ₁ and Vr ₂ are sent out via A ₁₁ and D/A ₁₂ .

Here, the resistors R ₁ , R ₂ and the differential amplifier A ₁₁ constitute a first control circuit, and the DAC/D/D/
Based on the reference voltage Vr ₁ from A ₁₁ , the voltage V ₁ is obtained by dividing the line voltage V _L of the transmission line L by resistors R ₁ and R ₂
Accordingly, the impedance of the transistor _Q11 is controlled in the direction of keeping the line voltage _VL constant, and thereby the line voltage _VL is kept at a constant value of, for example, 10V, regardless of the value of the line current _IL . I'm keeping it.

Also, resistors R ₄ , R ₅ and differential amplifier A ₁₂ are
A second control circuit is configured, and based on the reference voltage Vr ₂ from the DAC/D/A ₁₂ , the load circuit side voltage Vc of the resistor R ₃ is divided into the voltage V ₂ by the resistors R ₄ and R ₅ . Accordingly, the impedance of transistor _Q12 is controlled in such a way as to keep the value of current Ic flowing through resistor _R3 constant, regardless of the power supply current of each load circuit.
The current Ic is maintained at a constant value of 4 mA, for example.

Therefore, the resistors R ₁ and R ₂ are set to high resistance values,
Assuming that the current I ₁ passing through this can be ignored,
The current Is flowing through the resistor Rs is Is = I _L − Ic,
By setting Ic equal to the bias component of, for example, 4 mA, Is becomes only a signal component of, for example, 0 to 16 mA. Therefore, the terminal voltage Vs of the resistor Rs is averaged by the integrating circuit INT ₂ , and then the ADC/A/D ₁₁ into a digital signal and sends it to the control unit CNT ₂ , this becomes the transmission data SA ₁ corresponding to the analog value of the line current I _L.

In addition, the frequency component of the digital change is extracted from the terminal voltage Vs by the wave generator FL ₂ , and the frequency component of the digital change is extracted from the terminal voltage _Vs.
, compare it with the reference voltage Er ₂ set by resistors R ₆ and R ₇ , detect the change, and apply it to the waveform shaper.
When applied to the control unit CNT ₂ via WF ₂ , this transmits data corresponding to digital changes in the line current I _L.
This indicates S ₂ .

Therefore, these are converted and decoded in the control unit CNT ₂ , and the transmission data SA ₁
According to the received data of the serial digital signal
Send as RB ₁ and send data as SA ₂
If it is sent as analog signal reception data RB ₂ via the DAC/D/A ₁₃ , the sending data SA ₁ , SA ₂
reception is performed simultaneously.

In addition, in FIG. 3, negative feedback is applied to the differential amplifiers A ₁₁ and A ₁₂ by the above operation,
Since the conditions are V ₁ ≒Vr ₁ and V ₂ ≒Vr ₂ , the following equation holds true.

V ₁ =V _L R ₂ /R ₁ +R ₂ =Vr ₁ ∴V _L =Vr ₁ (1 + R ₁ /R ₂ ) ...(1) V ₂ =VcR ₅ /R ₄ +R ₅ =Vr ₂ ∴Vc = Vr ₂ (1+R ₄ /R ₅ ) ...(2) Here, Vr ₁ and Vr ₂ are stabilized as long as the data from the control unit CNT is constant, so V _L and Vc are also constant, and the following The formula is obtained.

Ic=V _L −Vc/R ₃ ...(3) In other words, Ic is constant.

On the other hand, line current I _L is expressed by the following equation.

I _L = I ₁ + I ₂ + I ₃ + Is = I ₁ + Ic + Is ... (4) Here, if I ₁ ≒ 0, Is = I _L - Ic ... (5) Therefore, if I _L is, for example, 4 For ~20mA, Ic
By setting Is = 4 mA, Is = 0 to 16 mA, and a maximum power current of 4 mA can be stably supplied to each load circuit without interfering with the reception of data indicated by Is.

In addition, on the device side of FIG. 2, the line current I _L is controlled by the constant current circuit of the differential amplifier A ₁ to the transistor Q ₁ .
Even if the input impedance on the receiving end changes, the current value will not be affected.

Regarding the above, when transmitting data such as actual measurement values to the device shown in Figure 2, the current Ic
The reference voltages Vr ₁ and Vr ₂ are kept constant.
The control unit CNT changes the DAC/
In order to change the data to D/A ₁₁ and D/A ₁₂ in an analog manner and in a pulsed manner by superimposing this, the line voltage V _L changes in an analog and digital manner accordingly. Transmission is performed by , and two pieces of data are simultaneously indicated by the atlog value and the code of digital change.

In other words, to keep the current Ic constant, the numerator of equation (3) should remain unchanged, and if V _L −Vc is V _R , then
The following equation can be obtained from equations (1) and (2).

V _L −Vc=V _R =Vr ₁ (1+R ₁ /R ₂ )−Vr ₂ (1+R ₄ /R ₅ ) ∴Vr ₂ = [Vr ₁ (1+R ₁ /R ₂ )−V _R ]1/(1+R ₄ /
_R5 )
...(11) Here, assuming the relationship of the following equation, R ₂ /R ₁ +R ₂ =R ₅ /R ₄ +R ₅ =K ...(12) From equations (11) and (12), the following equation A relationship is established.

Vr ₂ = (Vr ₁ 1/K-V _R )K = Vr ₁ -V _R・K ...(13) Therefore, while maintaining the relationship of equation (13), ADC・
By changing the data to A/D ₁₁ and A/D ₁₂ at the same time, it is possible to freely increase or decrease the line voltage V _L while keeping the current Ic at 4 mA, for example.
Transmission based on voltage changes can be performed while receiving based on current values.

In addition, if changes in voltage Vc affect the operation of each load circuit, insert a voltage stabilization circuit in the part where current I ₂ passes, and connect the circuit of resistors R ₄ and R ₅ to the input side of this circuit. Just connect.

As described above, for the purpose of transmission based on changes in _{the line} voltage V _L , in _FIG. Media control section
CNT ₂ , and the control unit CNT ₂ converts and encodes each of these inputs.
For example, if the transmission data SB ₁ is an analog value, and
After converting the transmitted data SB ₂ into a digital change,
Digital changes are superimposed and synthesized on the analog value, and the reference voltages Vr ₁ and Vr ₂ are simultaneously controlled according to the relationship of equation (13) according to this synthesized value, and the change in line voltage V _L shown in Fig. 1 is obtained. Send as.

Therefore, power is simultaneously supplied only through the two-wire transmission line, and two data items SA ₁ , SA ₂ and SB ₁ are transmitted by one opposing device.
SB ₂ transmission and reception will be performed, significantly reducing equipment costs and man-hours for maintenance and inspection.

FIG. 4 is a block diagram showing another embodiment, in which one device CEA is connected to one end of the transmission line L, and a plurality of other devices CE _B1 to CE _Bo are connected to the other end of the traditional line L. are connected in series with each other, and the device
The line current I _L is transmitted from CE _A in the same manner as in Fig. 1, and is simultaneously received by the devices CE _B1 to CE _Bo , and is also applied to a polling signal indicated by a digital change in the line current I _L , for example. Accordingly, a specified one of the devices CE _B1 to CE _Bo changes the corresponding one of the line voltages V _L1 to V _Lo as shown in Figure 1, thereby transmitting a response. .

Then, since the relationship is V _L = V _L1 + V _L2 +...V _Lo , the response transmission is received in the device CE _A , and the two data are the analog value and digital change of the line current I _L. The transmission and reception of two data based on the analog value and digital change of the line voltage V _L are simultaneously performed.

However, the transmission from device CE _A is transmitted from device CE _B1 to
While commonly received at CE _Bo ,
Since the transmissions from CE _B1 to CE _Bo are received only by the device CE _A , the analog value change range and absolute value of the line voltages V _L1 to V _Lo must be determined individually, or the address code can be determined by digital changes. Various two-way multiplex communication systems can be applied by means such as expressing.

Therefore, device CE _A and multiple devices CE _B1 ~
By simply connecting CE _Bo with one transmission line L, two pieces of data can be transmitted simultaneously from device CE _A to devices CE _B1 to _{CE Bo .} any of the equipment
Two pieces of data can be transmitted to CE _A at the same time, and the transmission path L can be shared.

However, in FIG. 1, it is preferable to make the digital change waveform both in the positive and negative directions, because it becomes an analog value by averaging, but it is also possible to make it only in the positive or negative direction depending on the conditions. The selection of waveforms indicating "0" and "1" is also arbitrary.

In addition, in FIGS. 2 and 3, controllable variable impedance elements such as field effect transistors and photocouplers may be used in place of the transistors Q ₁ , Q ₁₁ , and Q ₁₂ , and the resistors Rf and Rs ，
The same effect can be obtained by replacing R ₃ with an impedance element such as a diode, or by using a circuit with a current detection function instead of the resistor Rs.
SA ₁ , SA ₂ , SB ₁ , SB ₂ and received data RA ₁ ,
RA ₂ , RB ₁ , and RB ₂ depend on the conditions of the other device.
The ADC or DAC may be inserted or omitted, and the control circuits CNT ₁ and CNT ₂ may be configured by a combination of various logic circuits or may be configured by analog circuits.

In addition, in Fig. 3, DAC・D/A ₁₁ ,
Instead of using the D/A ₁₂ , the reference voltages Vr ₁ and Vr ₂ may be generated using a constant voltage diode or the like, and these may be switched during transmission.

In addition, the bias component of the line current I _L can be determined according to the required power supply current of the load circuit, and a motor etc. can be included in the load circuit, and in an industrial process, devices CE _B1 to _{CE Bo} can be Installed on the side of controlled equipment such as valves, pumps, dampers, etc.
Setting values, command information, etc. are sent from the installation CE _A , and the device
Current measured values, monitoring information, etc. may be transmitted from the CE _B1 to CE _Bo sides, but various modifications are possible, such as being applicable to various remote controls and remote monitoring.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to use a communication device that transmits data within a predetermined current value range of 4 to 20 mA through a two-wire transmission line.
Including this data, two pieces of data can be transmitted and received at the same time with a simple configuration, reducing equipment costs and maintenance man-hours, and providing remarkable effects in various remote control and monitoring.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention, Fig. 1 is a diagram showing changes in line current and line voltage, Fig. 2 is a block diagram showing a first communication device, and Fig. 3 is a diagram showing a second communication device. FIG. 4 is a block diagram showing another embodiment. V _L , V _L1 ~ V _Lo ... Line voltage, I _L ... Line current,
SA ₁ , SA ₂ , SB ₁ , SB ₂ ...Transmission data, RA ₁ ,
RA ₂ , RB ₁ , RB ₂ ... Received data, L ... Transmission line (2-wire transmission line), Q ₁ , Q ₁₁ , Q ₁₂ ... Transistor, Rf, Rs, R ₃ ... Resistor, A ₁ , _A11 , _A12 ...
Differential amplifier, CP ₁ , CP ₂ ... Comparator, CNT ₁ ,
CNT ₂ ...control unit, CE _A ...device (one communication device), CE _B1 to CE _Bo ...device (other communication device).

Claims (1)

[Claims] 1. In a communication device in which a first communication device and a second communication device are connected via a two-wire transmission path and signals are exchanged between the two communication devices, the first communication device A composite signal in which a pulse signal of a predetermined code corresponding to the second transmission data is superimposed on an analog signal having a value within a predetermined range corresponding to the first transmission data is supplied to the two-wire transmission line as a change in the line current value. a transmitting means for detecting the line voltage of the two-wire transmission line, and transmitting an analog signal according to the third transmission data sent from the second communication device and an analog signal according to the fourth transmission data sent from the detection output from the detection output; The second communication device detects the line current of the two-wire transmission line, and receives the signal sent from the first communication device from the detected output. receiving means for separating and outputting an analog signal corresponding to the first transmission data and a pulse signal corresponding to the second transmission data;
1. A communication device comprising: transmitting means for supplying a composite signal obtained by superimposing a pulse signal of a predetermined code corresponding to transmission data to a two-wire transmission line as a change in line voltage value.